Cellulolytic clostridia are important in the anaerobic digestion of agricultural residues and of MSW to produce biogas. An understanding of biological cellulose degradation is important for optimising the anaerobic digestion of these waste materials, either singly or in various combinations, and for the exploitation of potential energy crops such as Sorghum and Miscanthus, which could provide extra income for farmers.
The most widely used methods of waste matter treatment are dumping and incineration, both of which contribute to the greenhouse effect. The closed carbon cycle of biomethanisation is a promising way for mitigating the increase in atmospheric CO2 attendant on continued use of fossil fuels for energy. An additional benefit of biomethanisation is a reduction in the volume of solid residue requiring disposal. Moreover, the residue after digestion of some materials is an excellent fertiliser.
Biomethanisation of urban waste, sometimes mixed with agricultural residues, is now an industrial reality, but for cellulose-rich wastes bacterial cellulolysis remains a bottleneck. We seek to remove this bottleneck by improving the efficiency of cellulose hydrolysis. As a result, biomethanisation of urban waste could become both economically and ecologically attractive as an alternative to dumping or incineration.
Cellulolytic clostridia have surface protuberances called cellulosome and cellulolysis results from a cyclic process of adhesion colonisation, release and re-colonisation. Release occurs when the substrate is exhausted and/or adhesion sites on the insoluble cellulose fibrils are saturated. Once released, the organisms undergo carbon starvation and loss of viability or dormancy can ensue. The very recent realisation of this fact is a new and fundamentally important insight into the dynamics of anaerobic bacterial cellulolysis. Maintenance of viability of released cells is crucial for efficient re-colonisation. The objectives of the proposed research are to understand and deal with the periodic carbon starvation to which these bacteria are subjected.
The research team includes a geneticist, a physiologist and a SME engaged in anaerobic digestion of MSW. We will define the conditions giving optimal cellulolytic activity and viability, without dormancy (sporulation), of released bacteria. Mutants of Clostridium cellullyticum with enhanced starvation resistance and altered sporulation potential will be selected and the regulation of gene expression during carbon starvation elucidated. This information, together with the mutant strains we isolate, will be employed in the pilot plant to improve digestion of cellulosic materials in agricultural residues and MSW. A spin-off of the proposed research is that it may enable the precise roles of the many components of the bacterial cellulosome to be explored by creating defined mutations in their structural genes in vivo.
Funding SchemeCSC - Cost-sharing contracts